Imaging particulates, paper and process, and imaging of paper using dual wavelength light

ABSTRACT

The present invention provides dual wavelength imaging compositions, processes for forming dual wavelength imaging compositions, methods for forming images using dual wavelength imaging compositions and substrate (e.g., paper web) treated (e.g., coated) on one or both sides with dual wavelength imaging compositions. Also provided is a dual wavelength imaging particulate comprising a matrix of polymer material and containing: one or more image-forming agents; a photo-oxidizing agent which is activated at a first wavelength of light to cause the one or more image-forming agents to form one or more images; and a reducing agent which is activated at a second wavelength of light to cause termination of the formation of the one or more images.

STATEMENT OF JOINT RESEARCH AGREEMENT

In compliance with 37 C.F.R. §1.71(g) (1), disclosure is herein madethat the claimed invention is made pursuant to a Joint ResearchAgreement as defined in 35 U.S.C. 103 (c) (3), that is in effect on orbefore the date the claimed invention is made, and as a result ofactivities undertaken within the scope of the Joint Research Agreement,by or on the behalf of the International Paper Company and Spectra GroupLtd.

BACKGROUND

1. Field of the Invention

The present invention broadly relates to a composition comprising dualwavelength image-forming particulates which may be used with asubstrate. The present invention also broadly relates to a process forpreparing these dual wavelength image-forming particulates. The presentinvention additionally broadly relates to substrates treated on one orboth sides with this dual wavelength imaging particulate-containingcomposition. The present invention further broadly relates a process fortreating one or more sides of a substrate with these dual wavelengthimage-forming particulates. The present invention further broadlyrelates to a method for imaging of a substrate using these dualwavelength image-forming particulates.

2. Related Art

Electrophotography provides a non-impact printing technology for today'sreprographic industries. A representative electrophotographic printingor copying process normally creates images on a coated polymericsubstrate in five steps. These steps include: (1) depositing a uniformelectric charge onto a photoconductor drum; (2) creating anelectrostatic latent image on the photoconductor by exposing thephotoconductor to an oscillating narrow laser beam that is turned on andoff digitally or a stationary array of LED lights which are turned onand off digitally; (3) exposing the photoconductor to toner particlessuch that toner particles having the correct polarity adhere to theexposed latent image; (4) passing the medium to be printed between thephotoconductor and a transfer corona to cause the toner particles totransfer from the photoconductor to the medium; and (5) fixing (e.g.,fusing) the transferred toner particles on the medium.

For example, a form of electrophotographic printing is laser printing.In laser printing, there are essentially five steps. In the first step(charging), a primary charge roller projects an electrostatic chargeonto the photoreceptor, a revolving photosensitive drum or belt, whichis capable of holding an electrostatic charge on its surface as long asit hasn't been exposed to certain wavelengths of electromagneticradiation. In the second step (writing), a raster image processor (RIP)chip converts incoming images to a raster image suitable for scanningonto the photoreceptor. A laser (or laser diode) is aimed at a movingmirror, which directs the laser beam through a system of lenses andmirrors onto the photoreceptor wherever the laser strikes thephotoreceptor the charge is reversed, thus creating a latentelectrophotographic image on the photoreceptor surface. In the thirdstep (developing), the surface containing the latent image is exposed totoner, with the charged toner particles being electrostaticallyattracted to the photoreceptor where the laser wrote the latent image.In the fourth step (transferring), the photoreceptor is pressed orrolled over paper, thus transferring the image formed by the chargedtoner particles. In the fifth step (fusing), the paper with thetransferred image passes through a fuser assembly having rollers thatprovide heat and pressure to bond or fuse the toner particles of theformed image to the paper.

Instead of electrophotographic printing such as laser printing, ink jetprinters may be used. There are essentially three types of ink jetprinters. The first category, thermal ink jet or bubble jet printers,work by having a print cartridge with a series of tiny electricallyheated chambers constructed by photolithography. To produce an image,the printer runs a pulse of current through heating elements, causingsteam in a chamber to form a bubble, which then propels a droplet of ink(usually water-based, pigment-based or dye-based) onto the paper. Theink's surface tension pulls another charge of ink into the chamberthrough a narrow channel attached to an ink reservoir.

A second category, piezoelectric ink jet printers, uses a piezoelectricmaterial in an ink-filled chamber behind each nozzle instead of aheating element. When a voltage is applied, the crystal changes shape orsize, which generates a pressure pulse in the fluid, thus forcing adroplet of ink from the nozzle. This is essentially the same mechanismas in the thermal inkjet printer but generates the pressure pulse usinga different physical principle.

A third category, continuous ink jet printers, uses a high-pressure pumpthat directs liquid ink from a reservoir through a microscopic nozzle,thus creating a continuous stream of ink droplets. A piezoelectriccrystal causes the stream of liquid to break into droplets at regularintervals, which are then subjected to an electrostatic field created bya charging electrode as they form. The field is varied according to thedegree of drop deflection desired, thus resulting in a controlled,variable electrostatic charge on each droplet. The charged droplets arethen directed (deflected) to the receptor material to be printed byelectrostatic deflection plates, or are allowed to continue onundeflected to a collection gutter for reuse.

Technological advances in electrophotography and ink jet printers havebrought an increase in the popularity of color electrophotographicprinters and copiers, as well as color ink jet printer. Unlike amonochrome printer or copier wherein only a single toner or ink jetcartridge, i.e. black toner or ink jet cartridge, is employed, fullcolor printing or copying may require as many as four toner or inkdroplet cartridges which provide yellow, magenta, cyan, and black.Because a separate imaging process may be required for each of the fourtoner or ink printer cartridges, color printers and copiers may be muchslower and more expensive than their monochrome counterparts. Therecording media suitable for color printers and copiers may also need tomeet more stringent requirements to provide a true full-colorreproduction of the original.

Copying and printing using electrophotographic or ink jet processes doeshave some disadvantages, especially in terms of the toners and inks usedto impart the resulting images. In electrographic copying or printing,the toner particles may not fuse properly, thus creating a messy productthat can get on hands, clothes, etc. Depending on how much of the papercomprises the image, there may be some portion of the toner particlesthat are not adhered to the paper, but are instead collected as aresidue that eventually may need to be disposed of. In ink jet printing,there are the conflicting requirements for a coloring agent that willstay on the surface, yet provide rapid dispersement of the carrier. Mostink jet printer cartridges use aqueous inks (e.g., based on a mixture ofwater, glycol and some dyes or pigments) that may be difficult tocontrol on the surface of print media and therefore require may requirespecially coated media.

Accordingly, it would be desirable to develop a method of forming animage on a paper web or other substrate that provides for the high speedand high quality printed images without the deficiencies of ink jet andelectrophotographic methods of printing.

SUMMARY

According to a first broad aspect of the present invention, there isprovided an article comprising: a dual wavelength image-formingparticulate comprising a matrix of polymer material and containing: oneor more image-forming agents; a photo-oxidizing agent which is activatedat a first wavelength of light to cause the one or more image-formingagents to form one or more images; and a reducing agent which isactivated at a second wavelength of light to cause termination of theformation of the one or more images.

According to a second broad aspect of the present invention, there isprovided an imaging composition comprising:

-   -   a solvent; and    -   a plurality of dual wavelength image-forming particulates        present in the solvent, wherein each particulate comprises a        matrix of polymer material and contains:        -   one or more imaging agents; and        -   a photo-oxidizing agent which is activated at a first            wavelength of light to cause the one or more image-forming            agents to form one or more images; and        -   a reducing agent which is activated at a second wavelength            of light to cause termination of the formation of the one or            more images.

According to a third broad aspect of the present invention, there isprovided an article comprising:

-   -   a substrate having first and second surfaces; and    -   a plurality of image-forming particulates applied to at least        one of the first and second surfaces, each particulate        comprising a matrix of polymer material and containing:        -   one or more imaging agents; and        -   a photo-oxidizing agent which is activated at a first            wavelength of light to cause the one or more image-forming            agents to form one or more images in or on the substrate;            and        -   a reducing agent which is activated at a second wavelength            of light to cause termination of the formation of the one or            more images.

According to a fourth broad aspect of the present invention, there isprovided a process comprising the following steps of:

-   -   (a) providing a substrate having first and second surfaces; and    -   (b) providing a plurality of dual wavelength imaging        particulates, wherein the particulates each comprise a matrix of        polymer material and contain:        -   one or more imaging agents;        -   a photo-oxidizing agent which is activated at a first            wavelength of light to cause the one or more image-forming            agents to form one or more images; and        -   a reducing agent which is activated at a second wavelength            of light to cause termination of the formation of the one or            more images;    -   (c) treating at least one of the first and second surfaces of        the substrate of step (a) with the particulates of step (b).

According to a fifth broad aspect of the present invention, there isprovided a method comprising the following steps of:

-   -   (a) providing a dual wavelength imaging substrate comprising:        -   a substrate having a first surface and a second surface; and        -   a plurality of dual wavelength image-forming particulates            applied to at least one of the first and second surfaces,            wherein the particulates each comprise a matrix of polymer            material and contain:        -   one or more imaging agents;        -   a photo-oxidizing agent which is activated at a first            wavelength of light to cause the one or more image-forming            agents to form one or more images; and        -   a reducing agent which is activated at a second wavelength            of light to cause termination of the formation of the one or            more images;    -   (b) subjecting the dual wavelength imaging substrate of step (a)        to the first wave length of light that activates the        photo-oxidizing agent to cause the one or more imaging agents to        form one or more images in or on the substrate; and    -   (c) subjecting the imaged substrate of step (b) to the second        wave length of light that activates the reducing agent to cause        the termination of the formation of the one or more images.

According to a sixth broad aspect of the invention, there is provided aprocess for making a dual wavelength imaging composition comprising thefollowing steps:

-   -   (a) providing a solvent; and    -   (b) dispersing or suspending a plurality of dual wavelength        image-forming particulates in the solvent to form a dual        wavelength imaging composition, wherein each particulate        comprises a matrix of polymer material and contains:        -   one or more image-forming agents; a photo-oxidizing agent            which is activated at a first wavelength of light to cause            the one or more image-forming agents to form one or more            images; and        -   a reducing agent which is activated at a second wavelength            of light to cause termination of the formation of the one or            more images.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic flowchart illustrating general embodiments of aprocess for preparing a dual wavelength imaging composition, for coatinga paper web with the dual wavelength imaging composition according toembodiments of the present invention, and for imaging of the coatedpaper; and

FIG. 2 is a schematic diagram illustrating an embodiment of a method forcoating a paper web with a dual wavelength imaging composition accordingto the present invention using a metering rod size press.

DETAILED DESCRIPTION

It is advantageous to define several terms before describing theinvention. It should be appreciated that the following definitions areused throughout this application.

DEFINITIONS

Where the definition of terms departs from the commonly used meaning ofthe term, applicant intends to utilize the definitions provides below,unless specifically indicated.

For the purposes of the present invention, the term “substrate” refersto any material which may be treated with image-forming particulates orcompositions comprising same to provide articles which may form imageswhen exposed to light which activates the photo-oxidizing agent.Substrates may include webs, sheets, strips, etc., may be in the form ofa continuous roll, a discrete sheet, etc., and may comprise variousmaterials or combinations of materials, including, for example, plastics(polymers), paper webs, non-wovens, etc.

For the purposes of the present invention, the term “paper web” refersto a fibrous web that may be formed, created, produced, etc., from amixture, furnish, etc., from paper fibers, plus any other optionalpapermaking additives such as, for example, fillers, wet-strengthagents, optical brightening agents (or fluorescent whitening agent),etc. Paper webs may include an uncoated paper web, coated paper web,etc. The paper web may be in the form of a continuous roll, a discretesheet, etc.

For the purposes of the present invention, the term “paper fibers”refers to plant fibers derived from, for example, woody and nonwoodyfibers, and which may comprise cellulose, cellulose derivatives, etc.See also G. A. Smook, Handbook for Pulp and Paper Technologists (2^(nd)Edition, 1992), pages 2-8, the entire contents and disclosure of whichis herein incorporated by reference, for a general description of paperfibers and sources thereof.

For the purposes of the present invention, the term “treated substrate”refers to a substrate, (e.g., paper web) which has a sufficient loading(e.g., a coat weight of at least about 50 lbs/ton, for example, at leastabout 100 lbs/ton) of dual wavelength image-forming particulates presenton one or both sides or surfaces of the substrate (e.g., paper web) suchthat one or more images may be formed from the particulates. In oneembodiment, the loading of dual wavelength image-forming particulatesmay be present in an amount of up to about 500 lbs/ton (e.g., up toabout 200 lbs/ton) on one or both sides or surfaces of the substrate(e.g., paper web).

For the purposes of the present invention, the term “untreatedsubstrate” refers to a paper web which has a 0 or substantially 0loading of dual wavelength image-forming particulates present on one orboth sides or surfaces of the substrate.

For the purposes of the present invention, the term “single-side treatedsubstrate” refers to a substrate (e.g., paper web) which has dualwavelength image-forming particulates present on one, but not both,sides or surfaces of the substrate.

For the purposes of the present invention, the term “double-side coatedtreated substrate” refers to a substrate (e.g., paper web) which hasdual wavelength image-forming particulates present on both sides orsurfaces of the substrate.

For the purposes of the present invention, the term “calendered paper”refers to a paper web which has been subjected to calendering to, forexample, smooth out the paper for enabling image formation on the paper,and to increase the gloss on the paper surface. For example, calenderingmay involve a process of using pressure for embossing a smooth surfaceon the still rough paper surface. Calendering of paper may be carriedout on a calendar which may comprise a series of rolls at the end of apapermaking machine (on-line), or separate from the papermaking machine(off-line).

For the purposes of the present invention, the term “particulate” refersto a relatively tiny or small solid particle which may bespherical-shaped, oval-shaped, etc., which may be regular and/orirregular in shape, and which may range in size from less than about 10nm. to more than 100 microns in diameter and which comprises a matrix ofpolymer material, and optionally other components, for example,plasticizers, softening agents, tackifying agents, texturing agents,dispersing aids, etc., and which contains, encapsulates, has embedded ordispersed therein, etc., one or more image-forming agents, aphoto-oxidizing agent, a reducing agent, acids/coupler, electron donoragents, etc.

For the purposes of the present invention, the term “image-formingparticulate” refers to those particulates which comprise or arecomprised of a matrix of polymer material and which contain at least oneor more imaging agents, a photo-oxidizing agent, and a reducing agent,but which may contain other agents, for example, acids/couplers,electron donating agents, etc. When subjected to a first wavelength oflight, the photo-oxidizing agent is activated to cause the imagingagent(s) form, create, etc., the one or more images; when subjected to asecond wavelength of light, the reducing agent is activated to terminateformation, creation, etc., of the one or more images.

For the purposes of the present invention, the term “dual wavelengthimaging composition” refers to those compositions which comprise aplurality of image-forming particulates, which may additionally comprisesolvents, dispersing agents, suspending agents, etc., and which mayform, create, etc., one or more images. These dual wavelength imagingcompositions may impart other properties to a substrate (e.g., paperweb) besides forming, creating, etc., one or more images, for example,paper sizing properties, opacity, brightening, etc. For these otherproperties, these dual wavelength imaging compositions may include otheroptional paper additives, for example, paper starch binders, pigments,paper co-binders, optical brightening agents (or fluorescent whiteningagents), cationic dye fixing agents, anti-static agents, anti-scratchand mar resistance agents, bulking agents, etc. The imaging compositionmay be formulated as a solution, suspension, dispersion, emulsion, etc.,and may wholly or partly comprise water, e.g., an aqueous solution,suspension, dispersion, emulsion, etc.

For the purposes of the present invention, the term “polymer material”refers to one or more polymers that are used to form the particulate ofthe image-forming particulate, and which may be optionally included inthe dual light imaging composition to thicken the formulation, to adherethe formulation to the substrate (e.g., paper web), to be used, forexample, in conjunction with a starch binder as a paper sizing or binderagent, etc., or any combination thereof. Suitable polymer materials mayinclude synthetic or naturally occurring polymers (or a combination ofdifferent polymers), for example, polymer latexes such as styrenebutadiene rubber latexes, acrylic polymer latexes, polyvinyl acetatelatexes, styrene acrylic copolymer latexes, etc., proteinaceousadhesives such as, for example, casein or soy proteins, etc.; apolyvinyl alcohol (PVOH), etc., or a combination thereof. Examples ofsuitable polymer materials may include ethyl cellulose, polyvinylalcohol, polyvinyl chloride, polystyrene, polyvinyl acetate,poly-(methyl, propyl or butyl methacrylate), cellulose acetate,cellulose butyrate, cellulose acetate butyrate, cellulose nitrate,chlorinated rubber, copolymers of the above vinyl monomers, etc. Thepolymer material may be present in an amount of, for example, from about0.5 to about 200 parts by weight, per part of the combined weight of theimage-forming agent, e.g., leuco dye. Generally from about 5 to about 20parts by weight may be used. Cellulose esters, such cellulose, acetatebutyrate, etc., may be particularly suitable polymer materials for useherein.

For the purposes of the present invention, the term “image-formingagent” refers to an agent which is capable of forming an image(s) on asubstrate (e.g., paper web) when exposed to an appropriate wavelength oflight, and in the presence of a photo-oxidizing agent. The image formedmay be text (e.g., a letter and/or number), a graphic, object, photo,picture, etc. Image-forming agents may include one or more dyes, forexample, leuco dyes, other light activated dyes, light activatedcolorants, light activated pigments, etc. The amount of image-formingagent used that may provide suitable imaging characteristics will dependupon a variety of factors, including the agent use, the substrate thatthe agent is used with, the particular image-forming conditions, etc.For example, in the case of leuco dyes, amounts from about 0.1 to about10% (e.g., from about 1 to about 5%) of the particulate solids may beused.

For the purposes of the present invention, the term “leuco dye” refersto compounds which are normally colorless or slightly colored but, whenoxidized, may form or are capable of forming different colors which mayencompass almost the entire visible region. The leuco dyes which may beused in embodiments of the present invention include, for example, thosewhich are described in U.S. Pat. No. 3,445,234 (Cescon et al.) issuedMay 20, 1969 (the entire disclosure and contents of which are herebyincorporated by reference), and some examples thereof are illustrated asfollows: (1) aminotriarylmethanes; (2) aminoxanthenes; (3)aminothioxanthenes; (4) amino-9,10-dihydroacridines; (5)aminophenoxazines; (6) aminophenothiazines; (7) aminodihydrophenazines;(8) aminodiphenylmethanes; (9) leucoindamines; (10) aminohydrocinnamicacids (cyanoethane, leucomethine); (11) hydrazines; (12) leucoindigoiddyes; (13) amino-2,3-dihydroanthraquinones; (14)tetrahalo-p,p′-biphenols; (15)2-(p-hydroxyphenyl)-4,5-diphenylimidazoles; and (16) phenethylanilines.Of these leuco dyes, (1) to (9) form dyes when they lose one hydrogenatom, and (10) to (16) dyes when they lose two hydrogen atoms.Illustrative leuco dyes may include Crystal Violet,tris(4-diethylamino-o-tolyl)methane,bis(4-diethylamino-o-tolyl)phenylmethane,bis(4-diethylamino-o-tolyl)-thienyl-2-methane,bis(2-chloro-4-diethylaminophenyl)phenylmethane,2-(2-chlorophenyl)amino-6-N,N-dibutylamino-9-(2-methoxycarbonyl)phenylxanthene,2-N,N-dibenzylamino-6-N,N-diethylamino-9-(2-methoxycarbonyl)phenylxanthene,benzo[a]-6-N,N-diethylamino-9-(2-methoxycarbonyl)phenylxanthene,2-(2chloro-phenyl)-amino-6-N,N-dibutylamino-9-(2-methylphenylcarboxamido)phenylxanthene,3,6-dimethoxy-9(2-methoxycarbonyl)phenylxanthene,3,6-diethoxyethyl-9-(2-methoxycarbonyl)phenylxanthene, benzoylleucomethylene blue, 3,7-bis-diethylaminophenoxazine, etc. Suitableaminotriarylmethanes may include, for example, the acid salts ofaminotriarylmethanes wherein at least two of the aryl groups are phenylgroups having: (a) an R₁R₂N-substituent in the position para to the bondto the methane carbon atom wherein R₁ and R₂ are each groups selectedfrom hydrogen, C₁ to C₁₀ alkyl, 2-hydroxyethyl, 2-cyano-ethyl, benzyl,etc.; and (b) a group ortho to the methane carbon atom which is selectedfrom lower alkyl(C₁₋₄), lower alkoxy(C₁₋₄, fluorine, chlorine, bromine,etc.; and the third aryl group may be the same as or different from thefirst two, and when different may be selected from: (a) phenyl which maybe substituted with lower alkyl, lower alkoxy, chloro, diphenylamino,cyano, nitro, hydroxy, fluoro, bromo, etc.; (b) naphthyl which may besubstituted with amino, di-lower alkylamino, alkylamino, etc.; (c)pyridyl which may be substituted with alkyl, etc.; (d) quinolyl; (e)indolinylidene which may be substituted with alkyl, etc. R₁ and R₂ maybe hydrogen, alkyl of 1-4 carbon atoms, etc. Leuco dyes may be presentin an amount of, for example, from about 0.1 to about 10% by weight,such as from about 1 to about 5% by weight, of the solids in the dualwavelength imaging composition. With the leuco form of dyes which haveamino or substituted amino groups within the dye structure and which arecharacterized as cationic dyes, an amine salt-forming mineral acid,organic acid, or an acid from a compound supplying the acid may beemployed (also referred to as “couplers”). The amount of acid/couplermay vary, for example, in the range of from about 0.33 to about 1 mol,per mol of amino nitrogen in the dye. In some embodiments, the quantityof acid/coupler is in the range of, for example, from about 0.5 to about0.9 mol, per mol of amino nitrogen. Representative acids/couplers whichmay form the required amine salts may include hydrochloric acid,hydrobromic acid, sulfuric acid, phosphoric acid, acetic acid, oxalicacid, p-toluenesulfonic acid, trichloroacetic acid, trifluoroaceticacid, perfluoroheptanoic acid, etc. Other acids such as “Lewis acids” oracid sources which may be employed as acids/couplers in the presence ofwater or moisture may include zinc chloride, zinc bromide, ferricchloride, etc. Representative leuco dye salts may includetris-(4-diethylamino-o-tolyl) methane zinc chloride,tris-(4-diethylamino-o-tolyl) methane oxalate,tris-(4-diethylamino-o-tolyl) methane p-toluenesulfonate, etc.

For the purposes of the present invention, the term “photo-oxidizingagent” refers to an agent or agents which may be capable of generatingradicals upon irradiation with light which may in turn oxidize animage-forming agent, (e.g., a leuco dye). As described in U.S. Pat. No.4,252,887 (Dessauer), issued Feb. 24, 1981, the entire disclosure andcontents of which is hereby incorporated by reference. Some examples ofthe photo-oxidizing agents may include lophine dimer compounds such as2,4,5-triarylimidazole dimers (see formula below) as described in U.S.Pat. No. 4,247,618 (Dessauer et al.), issued Jan. 27, 1981, and U.S.Pat. No. 4,311,783 (Dessauer), issued Jan. 19, 1982; azide compoundssuch as 2-azidobenzoxazole, benzoylazide, 2-azidobenzimidazole, etc., asdescribed in U.S. Pat. No. 3,282,693 (Sagura et al.), issued Nov. 1,1966; pyridinium compounds such as3′-ethyl-1-methoxy-2-pyridothiacyanine perchlorate,1-methoxy-2-methylpyridinium-p-toluenesulfonate, etc., organic halogencompounds such as N-bromosuccinimide, tribromomethyl phenyl sulfone,diphenyliodide, 2-trichloromethyl-5-(p-butoxystyryl)-1,3,4-oxadiazole,2,6-di-trichloromethyl-4-(p-methoxyphenyl)triazine, etc., as describedin U.S. Pat. No. 3,615,568 (Jenkins), issued Oct. 26, 1971; azidepolymers as described in Nihon Shashin Gakkai 1968-nen Syunki KenkyuHappyokai Koenyoshisyu, p 55 (1968), the entire disclosure and contentsof all of the aforementioned documents being hereby incorporated byreference. Of these compounds, lophine dimer compounds and organichalogen compounds may be used, with combinations of two such compoundsproviding a high sensitivity, for example, a combination of: A) an2,4,5-triphenylimidazolyl dimer of the formula:

wherein R₁ is 2-bromo, 2-chloro, 2-fluoro, 2-alkyl of 1 to 4 carbonatoms, 2,4-dichloro, etc.; R₂ is 2-bromo, 2-chloro, 2-fluoro, 4-chloro,2-alkyl of 1 to 4 carbon atoms, 2-cyano, 2-alkoxy, etc., wherein thealkyl radical is of 1 to 4 carbon atoms; R₃ is 3,4-dimethoxy,3,4-diethoxy, 2,3-dimethoxy, 2,4,6-trimethoxy, 4-alkoxy, etc., whereinthe alkyl radical is of 1 to 4 carbon atoms, 3,4-methylenedioxy, etc.;an imidazolyl dimer having an extinction coefficient determined inmethylene chloride at from about 10⁻⁵ to about 10⁻³ mol/liter at about350 nm of at least about 4000 liters/mol-cm and at about 400 nm of atleast about 250 liters/mol-cm; and at least one compound taken from thegroup consisting of (B1) a leuco dye that is oxidizable to dye by theimidazolyl radicals; and (B2) an addition polymerizable ethylenicallyunsaturated monomeric compound. The image-forming particulates of thepresent invention may contain the specific 2,4,5-triphenylimidazolyldimers and either a dye in its leuco form, or, in the event that theimage-forming agent is photopolymerizable, a compound having ethylenicunsaturation. Both the leuco dye and ethylenically unsaturated compoundmay be present in the image-forming particulate. Image-formingparticulates containing the specific 2,4,5-triphenylimidazolyl dimer andleuco dye may be stabilized to prevent color build-up in the nonimageareas. The following processes may be used to achieve suchstabilization: treatment with a solution containing a free radical trap,e.g., hydroquinone, phenidone, etc.; inclusion of precursors ofhydroquinone which lead to its generation by heat, e.g., a dihydropyranadduct of ditertiarybutylhydroquinone; inclusion of quinones(photoactivatible oxidants) and hydrogen donor compounds (reductantcomponents) which may be employed to generate hydroquinones by lightexposure, for example, at a wavelength distinct from the image-formingexposure; photopolymerizable compounds which act as plasticizers topromote image formation until polymerized when they limit diffusion ofimage-forming species and prevent formation of images, etc. Additionalcomponents which may be present in the image-forming particulates mayinclude: anti-blocking agents, dyes, and white and colored pigmentswhich do not act as sensitizers, etc. In a photopolymerizablecomposition containing the specific 2,4,5-triphenylimidazolyl dimer andaddition polymerizable ethylenically unsaturated compound there may bepresent a free radical producing, electron donor agent hydrogen donor(hydrogen donor), e.g., organic amines, mercaptans, certainhalogen-containing compounds, active methylene compounds, etc. Thespecific triphenylimidazolyl dimers may be present in an amount of, forexample, from about 0.1 to about 10.0% by weight, such as from about 1to about 5% by weight, of the solids in the dual wavelength imagingcompositions. In preparing embodiments of the dual wavelength imagingformulations of the present invention, the leuco dye and thephoto-oxidizing agent may be mixed in a proportion (i.e., molar ratio)of from about 0.2:1 to about 5:1, for example from about 0.5:1 to about2:1.

For the purposes of the present invention, the term “reducing agent”refers to an agent that may inhibit the activation of thephoto-oxidizing agent, thus terminating the formation of the one or moreimages. A reducing agent allowed to exist in the vicinity of thephoto-oxidizing agent may immediately reduce the activatedphoto-oxidizing agent so it loses the ability to oxidize theimage-forming agent (e.g., leuco dye). That is, such reducing agentfunctions as a so-called free radical scavenger which may trap the freeradical of the activated photo-oxidizing agent. As specific examples ofthe reducing agent, there are illustrated hydroquinone compounds andaminophenol compounds which have a hydroxy group in the benzene ring andat least another hydroxy group or amino group in a different position ofthe benzene ring, as described in U.S. Pat. No. 3,042,515 (Wainer),issued Jul. 3, 1962; cyclic phenylhydrazide compounds, compoundsselected from among guanidine derivatives, alkylenediamine derivativesand hydroxyamine derivatives, as described in JP-B-62-39738, the entiredisclosure and contents of all of the aforementioned documents of whichis hereby incorporated by reference. These compounds may be used aloneor as a combination of two or more. However, these examples are notlimitative, and other known reducing substances which possess thefunction of acting on or reacting with oxidants may also be used. Forexample, the redox couple may comprise 9,10-phenanthrenequinone, aloneor in admixture with 1,6- and 1,8-pyrenequinone as the oxidant, with thereductant component comprising from about 10 to 100% of an acyl ester oftriethanolamine of the formula:

where R is alkyl of 1 to 4 carbon atoms, and from 0 to about 90% of a C₁to C₄ alkyl ester of nitrilotriacetic acid or of3,3′,3′-nitrilotripropionic acid. Triethanolamine triacetate anddibenzylethanolamine acetate are illustrative of such reductantcomponents.

For the purposes of the present invention, the term “electron donor(hydrogen donor) agent” refers to an agent having a reactive atom,usually hydrogen, which is removable and which in the presence of theradical of the substituted 2,4,5-triphenylimidazolyl dimer yields aradical which reacts with the monomeric compound to initiate growth ofpolymer chains. Free radical producing, electron donor agents and activemethylene compounds that may be used in the dual wavelength imagingcompositions are described in, for example, column 2, line 50 to column3, line 3, of U.S. Pat. No. 3,479,185 (Chambers, Jr.), issued Nov. 18,1969, the entire disclosure and contents of which are herebyincorporated by reference. Examples of suitable electron or hydrogendonor compounds may include compounds that form a stable compositionwith the hexaphenylbiimidazole compound in the dark. The agent may be anamine, e.g., a tertiary amine. The amine-substituted leuco dyes may beuseful, for example, those having at least one dialkylamino group. Also,any leuco triphenylamine dye or various salts of the dye, e.g., the HClsalt of the leuco blue dye can be used. Illustrative dyes may includetris-(4-N,N-diethylamino-o-tolyl)-methane trihydrochloride,bis(4-N,N-diethylamino-o-tolyl)triphenylmethane,bis(4-N,N-diethylamino-o-tolyl) methylenedioxyphenylmethane, leuconeutral shase dye, i.e., bis(4-N,N-diethylamino-o-tolyl)-benzylthiophenylmethane, Leuco Malachite Green (C.I. Basic Green 4), leucoforms of Crystal Violet, Brilliant Green (C.I. Basic Green 1), VictorialGreen 3B (C.I. Basic Green 4), Acid Green GG (C.I. Acid Green 3), MethylViolet (C.I. Basic Violet 1), Rosaniline (C.I. Basic Violet 14), etc.The salt forms, e.g., HCl salt, salts with a Lewis acid, sulfuric acidsalts, p-toluene sulfonic acid salts, etc., of the leuco dye ispreferred for use. Additional suitable, electron donor agents which canbe used singly or in combination include aniline, N-methylaniline,N,N-diethylaniline, N,N-diethylcresidine, triethanolamine, ascorbicacid, 2-allylthiourea, sarcosin, N,N-diethylglycine, trihexylamine,diethylcyclohexylamine, N,N,N′,N′-tetramethylethylenediamine,diethylaminoethanol, ethylaminoethanol,N,N,N′,N′-ethylenediaminotetracetic acid, N-methylpyrrolidone,N,N,N′,N″,N″-pentamethyldiethylenetriamine, N,N-diethylxylidene,N,N′-dimethyl-1,4-piperazine, N-β-hydroxyethylpiperidine,N-ethylmorpholine, and related amino compounds. While the tertiaryamines and especially the aromatic tertiary amines having at least oneCH₂ group adjacent to the nitrogen atoms may be useful, a combination oftwo radical generating agents such as a tertiary amine, e.g.,N,N-dimethylaniline, and a secondary amine, e.g., N-phenylglycine, mayalso be useful. In a dual wavelength imaging composition containing thehexaphenylbiimidazole, monomeric compound and electron donor agent, thelight-sensitivity, speed, or degree of polymerization may be dependenton the concentration of the hexaphenylbiimidazole and electron donoragent. Useful dual wavelength imaging compositions may be limited inpart by the solubilities of the components. When a leuco dye is used asthe electron donor agent, a mole ratio of leuco dye to thehexaphenylbiimidazole of, for example, from about 1.0 to about 1.4 mayprovide the best results as to photospeed and stability.

For the purposes of the present invention, the term “plasticizer” refersto the conventional meaning of this term as an agent which softens thepolymer material, thus providing flexibility, durability, etc. Suitableplasticizers for use herein are disclosed in, for example, column 10,lines 20 to 73 of U.S. Pat. No. 3,658,543 (Gerlach, Jr., et al.), issuedApr. 25, 1972, the entire disclosure and contents of which are herebyincorporated by reference. Suitable plasticizers may includepolyethylene glycols such as the commercially available carbowaxes, andrelated materials, such as substituted phenolethylene oxide adducts, forexample, polyethers obtained from o-, m- and p-cresol, o-, m- andp-phenylphenol and p-nonylphenol, including commercially availablematerials such as the “Igepal” alkyl phenoxy polyoxyethylene ethanols,(e.g., nonylphenoxypoly(ethyleneoxy)-ethanol); acetates, propionates,butyrates and other carboxylate esters of ethylene glycol, diethyleneglycol, glycerol, pentaerythritol and other polyhydric alcohols; alkylphthalates and phosphates such as dimethyl phthalate, diethyl phthalate,dioctyl phthalate, tributyl phosphate, trihexyl phosphate, trioctylphosphate, triphenyl phosphate, tricresyl phosphate and cresyl diphenylphosphate; sulfonamides such as N-ethyl-p-toluenesulfonamide; etc. Theplasticizers may be used in a concentration in the range of, forexample, from about 1:20 to about 5:3, such as from about 1:5 to about1:2, based on the weight of polymer material used.

For the purposes of the present invention, the term “solvent,” unlessspecified otherwise, refers not only to a liquid in which a solute isdissolved, but also to a liquid in which solids are suspended ordispersed. A solvent is any liquid, including a liquid solution, inwhich solids of the present invention are dispersed. Suitable solventsfor use herein include aqueous solvents (e.g., water, or water withanother water-miscible solvent), etc.

For the purposes of the present invention, the term “solids portion” ofa dual wavelength imaging composition refers to the particulates of thepresent invention and anything contained in or bound to the particulatesof the present invention. The solids portion may include polymermaterials, plasticizers, photo-oxidizing agents, reducing agents,image-forming agents (e.g., leuco dyes), acids/couplers, etc. Theparticulates of the present invention may be dissolved or suspended in aliquid solvent to form a coating that is applied to one or both sides ofa substrate (e.g., paper web).

For the purposes of the present invention, the term “paper filler”refers commonly to mineral products (e.g., calcium carbonate, such asprecipitated calcium carbonate (PPC), granulated calcium carbonate(GCC), kaolin clay, etc.) which may be used in paper making to reducematerials cost per unit mass of the paper, increase opacity, increasesmoothness, etc. These mineral products may be finely divided, forexample, in the size range of up to about 20 microns (e.g., from about0.5 to about 5 microns). See also G. A. Smook, Handbook for Pulp andPaper Technologists (2^(nd) Edition, 1992), page 225, the entirecontents and disclosure of which is herein incorporated by reference,for a general description of paper fillers that may be useful herein.

For the purposes of the present invention, the term “paper starchbinder” refers to a binder agent for paper webs which comprises starch,a starch derivative, etc., or a combination thereof. Suitable starchbinders may be derived from a natural starch, e.g., natural starchobtained from a known plant source, for example, wheat, maize, potato,tapioca, etc. The starch binder may be modified (i.e., a modifiedstarch) by one or more chemical treatments known in the paper starchbinder art, for example, by oxidation to convert some of —CH.₂OH groupsto —COOH groups, etc. In some cases the starch binder may have a smallproportion of acetyl groups. Alternatively, the starch binder may bechemically treated to render it cationic (i.e., a cationic starch) oramphoteric (i.e., an amphoteric starch), i.e., with both cationic andanionic charges. The starch binder may also be a starch converted to astarch ether, or a hydroxyalkylated starch by replacing some —OH groupswith, for example, —OCH₂CH₂OH groups, —OCH2CH₃ groups, —OCH₂CH₂CH₂OHgroups, etc. A further class of chemically treated starch binders whichmay be used are known as the starch phosphates. Alternatively, rawstarch may be hydrolyzed by means of a dilute acid, an enzyme, etc., toproduce a starch binder in the form of a gum of the dextrin type. Seealso G. A. Smook, Handbook for Pulp and Paper Technologists (2^(nd)Edition, 1992), page 285, the entire contents and disclosure of which isherein incorporated by reference, for a general description of starchbinders that may be useful herein.

For the purposes of the present invention, the term “paper pigment”refers to a material (e.g., finely divided particulate matter) which maybe used or may be intended to be used to affect optical properties ofthe paper web. Paper pigments may also function as paper fillers (andvice versa), and may include titanium dioxide, pigmented PCC, pigmentedGCC, etc. See also G. A. Smook, Handbook for Pulp and PaperTechnologists (2^(nd) Edition, 1992), pages 286-88, the entire contentsand disclosure of which is herein incorporated by reference, for ageneral description of paper pigments that may be useful herein.

For the purposes of the present invention, the term “cationic dye fixingagents” refers to cationic salts which may complex with anionic dyes toform an agglomerate, complex, aggregate, etc. These cationic salts mayinclude metal salts such alkali metal salts, alkaline earth metal salts,transition metal salts of, for example, halides, sulfates, silicates,etc., such as sodium chloride, calcium chloride, magnesium chloride,aluminum chloride, sodium sulfate, aluminum sulfate, potassium chloride,sodium aluminum sulfate, vanadium chloride, magnesium sulfate, sodiumsilicates, etc.

For the purposes of the present invention, the term “anti-static agents”refers to conductive materials which lower surface and volumeresistivity. Suitable “anti-static agents” may include quaternary salttype cationic anti-static agents, for example, alkali metal and ammoniumsalts of poly-(styrene sulfonic acid), sulfonated styrene/maleicanhydride copolymer, poly(acrylic acid), poly-(methacrylic acid),poly(vinyl phosphate) and free acids thereof, copolymers of dimethylallyl ammonium chloride and diacetone acrylamide, quaternary acrylics,copolymers of dimethyl diallyl ammonium chloride and N-methylacrylamide,poly(dimethyl diallyl) ammonium chloride, quaternary cellulose acetate,etc. These anti-static agents may be included in the coatingcompositions in amounts of from about 0.5 to about 25% by weight, moretypically in amounts of from about 1 to about 10% by weight. Papers usedherein may have a brightness of about 75 or greater.

For the purposes of the present invention, the term “brightness” refersto the diffuse reflectivity of paper, for example, at a mean wavelengthof light of 457 nm. As used herein, brightness of the paper web may bemeasured by, for example, in terms of GE Brightness or ISO Brightness.

For the purposes of the present invention, the term “opacity” refers tothe ability of a paper to hide things such as images on subsequentsheets or printed on the back, e.g., to minimize, prevent, etc.,show-through, etc. As used herein, opacity of the paper web may bemeasured by, for example, in terms of TAPPI opacity and show-through.TAPPI opacity may be measured by T425 om-91.

For the purposes of the present invention, the term “print quality”refers to those factors, features, characteristics, etc., that mayinfluence, affect, control, etc., the appearance, look, form, etc., ofthe formed image on the paper. As used herein, print quality of thepaper web may be measured by, for example, in terms of one or more of:(1) print density/contrast (e.g., for BW/color/monochrome); (2) colorgamut or color richness; (3) print gloss or print mottle; (4) etc. Forexample, black optical print density may be measured by TAPPI method1213 sp-03. Print mottle may be measured based on 2nd cyan valuesaccording to the method disclosed in U.S. Published Application No.20060060317 (Roding, et al.), published Mar. 23, 2006, the disclosureand contents of which are herein incorporated by reference. Papers usedherein may have print quality of about 0.65 or greater, for example,about 0.8 or greater or about 1.0 or greater.

For the purposes of the present invention, the term “paper smoothness”refers to the extent to which the paper surface deviates from a planaror substantially planar surface, as affected by the depth of the paper,paper width, numbers of departure from that planar surface, etc. As usedherein, the paper smoothness of a paper web may be measured by, forexample, in terms of Sheffield smoothness. Sheffield smoothness may bemeasured by TAPPI test method T 538 om-01, in Sheffield Units (SUs).Papers used herein may have a smoothness of about 450 SUs or greater.

For the purposes of the present invention, the term “liquid” refers to anon-gaseous fluid composition, compound, material, etc., which may bereadily flowable at the temperature of use (e.g., room temperature) withlittle or no tendency to disperse and with a relatively highcompressibility.

For the purposes of the present invention, the term “solids content”refers to the percentage of non-volatile, non-liquid components (byweight) that are present in the composition, coating, etc.

For the purposes of the present invention, the term “size press” refersto a device, equipment, machine, etc., which may be used to treat,apply, coat, etc., a dual wavelength imaging composition to one or moresides or surfaces of the substrate (e.g., paper web), for example, justafter the paper web has been dried for the first time. Size presses mayinclude a puddle size press, a metering size press, etc. See also G. A.Smook, Handbook for Pulp and Paper Technologists (2^(nd) Edition, 1992),pages 283-86, the entire contents and disclosure of which is hereinincorporated by reference, for a general description size presses thatmay be useful herein.

For the purposes of the present invention, the term “flooded nip sizepress” refers to a size press having a flooded nip (pond), also referredto as a “puddle size press.” Flooded nip size presses may includevertical size presses, horizontal size presses, etc.

For the purposes of the present invention, the term “metering sizepress” refers to a size press that includes a component for spreading,metering, etc., deposited, applied, etc., a coating of a dual wavelengthimaging composition on a substrate (e.g., paper web) side or surface.Metering size presses may include a rod metering size press, a gatedroll metering size press, a doctor blade metering size press, etc.

For the purposes of the present invention, the term “rod metering sizepress” refers to metering size press that uses a rod to spread, meter,etc., a coating of a dual wavelength imaging composition on substrate(e.g., paper web). The rod may be stationary or movable relative to thesubstrate.

For the purposes of the present invention, the term “gated roll meteringsize press” refers to a metering size press that may use a gated roll,transfer roll, soft applicator roll, etc. The gated roll, transfer roll,soft applicator roll, etc., may be stationery relative to the substrate(e.g., paper web), may rotate relative to the substrate, etc.

For the purposes of the present invention, the term “doctor blademetering size press” refers to a metering press which may use a doctorblade to spread, meter, etc., a coating of a dual wavelength imagingcomposition on the substrate (e.g., paper web) surface.

For the purposes of the present invention, the term “room temperature”refers to the commonly accepted meaning of room temperature, i.e., anambient temperature of 20° to 25° C.

For the purpose of the present invention, the term “treating” withreference to the of dual wavelength imaging composition may includedepositing, applying, spraying, coating, daubing, spreading, wiping,dabbing, dipping, etc., wherein the composition may remain (partially orwholly) on the surface of the substrate (e.g., paper web), may(partially or wholly) penetrate the surface, impregnate the interior,etc., of the substrate (e.g., paper web), etc.

For the purposes of the present invention, the term “coating” refers toone or more layers, coverings, films, skins, etc., formed, created,prepared, etc., from a dual wavelength imaging composition which remainspredominantly on the surface(s) of the substrate (e.g., paper web).

For the purposes of the present invention, the term “remainspredominantly on the surface(s) of the substrate (e.g., paper web)”refers to a coating of a dual wavelength imaging composition whichremains primarily on the surface of the substrate, and not beingabsorbed by or into the interior of the substrate (e.g., paper web).

For the purpose of the present invention, the term “treating” withreference to the dual wavelength imaging composition may includedepositing, applying, spraying, coating, daubing, spreading, wiping,dabbing, dipping, etc.

DESCRIPTION

Embodiments of the present invention may include dual wavelengthimage-forming particulate comprising a matrix of polymer material andcontaining: one or more image-forming agents; a photo-oxidizing agentwhich is activated at a first wavelength of light to cause the one ormore image-forming agents to form one or more images; and a reducingagent which is activated at a second wavelength of light to causetermination of the formation of the one or more images. Embodiments ofthe present invention may also comprise imaging compositions comprisinga solvent and a plurality of dual wavelength image-forming particulatespresent in the solvent. Embodiments of the present invention may alsoinvolve a process for treating at least one side or surface of asubstrate (e.g., paper web) with these dual wavelength image-formingparticulates. Embodiments of the present invention may also comprise asubstrate (e.g., paper web) treated (e.g., coated) with these dualwavelength image-forming particulates on at least one side or surface ofthe substrate. Embodiments of the present invention may also involve amethod wherein a substrate (e.g., paper web) treated with these dualwavelength image-forming particulates on at least one side or surface ofthe substrate are then subjected to a first wave length of light to formone or more images on the substrate, and then subjected to a second wavelength of light to terminate the formation of any further images.Embodiments of the present invention may also involve processes forforming the dual wavelength imaging composition.

Embodiments the dual wavelength image-forming particulates, imagingcompositions, processes, methods, etc., of the present invention mayprovide several advantageous properties and benefits, including: (1) adual wavelength-sensitive color forming formulation which may initiallydevelop one or more color images upon exposure to one wavelength oflight, followed by termination of color formation by exposure to asecond and different wavelength of light; (2) a dual wavelength imagingformulation comprising image-forming polymeric particulates which may beprocessed economically and efficiently; (3) the ability of image-formingpolymeric particulates in the dual wavelength imaging formulation to bedispersed in water, a starch/water paper sizing composition, etc.; (4)the ability to provide appropriate particulate size reduction of theimage-forming polymeric particulates in the dual wavelength imagingformulation; (5) coating of the particulate size-reduced dual wavelengthimaging formulation onto one or both sides or surfaces of a substrate(e.g., paper web); (6) the ability to sequentially expose the treatedsubstrate (e.g., coated paper web) to a first wavelength of light todevelop one or more color images, followed by exposure to a secondwavelength of light to terminate further development of color image(s),for example, where color image formation is triggered by UV light, withsubsequent visible light exposure to prevent further color imageformation in areas unexposed to UV light; etc.

The combination of the above properties and benefits, and the ability touse these embodiments in on-line paper manufacturing process may allowproduction of, for example, one-of-a-kind paper with unique set ofproperties, which may be very beneficial for image creation on the papersurface in the absence of any ink transfer. Embodiments of the presentinvention may also allow substitution for thermal printing inpoint-of-purchase applications, thus reducing the amount of energyneeded to print, improve the quality of the printed receipt in terms ofits durability and archival storage, etc. Embodiments of the presentinvention may also allow for shared office or home office use, thuspotentially replacing traditional laser transfer and ink jet transferprinters.

Embodiments of dual wavelength image-forming particulates useful in theembodiments of the dual wavelength imaging compositions of the presentinvention may comprise thermoplastic or thermosettable particulatematrices. The image-forming particulates may comprise a polymericmatrix, (e.g., shell, sphere, substrate, etc.) in which are contained(e.g., embedded, incorporated, encapsulated, associated, etc.) theimage-forming agents, for example, dyes (e.g., leuco dyes),photo-oxidizing agents, reducing agents, plasticizers, acids/couplers,electron donating agents, etc. The particulates may be free-flowing;that is, they do not agglomerate and are detached from each other. Inone embodiment of the present invention, the particulates may also befusible or crosslinkable with each other and/or a surrounding matrix.

In one embodiment, the dual wavelength image-forming particulates may beprepared from a polymer, co-polymer, or polymer blend solvated by anappropriate solvent, and then combined with the image-forming agents andassociated photo-oxidizing and reducing agents, etc. Optionally,crosslinkers, catalysts, plasticizers, stabilizers, and other desirableadditives may be added to the mixture. The mixture may then be atomizedinto air, or homogenized in a second immiscible liquid, to producemicroscopic droplets. Either by evaporation or liquid-liquid extraction,the solvent may then be removed from the droplets, precipitating thepolymer from solution and effectively solidifying the droplets intohard-walled polymeric particulates containing the image-forming agentsand other optional additives.

Image-forming particulates may be produced by first forming a solutioncomprising the polymer or polymer mixture that is to form theparticulate matrix, the image-forming agents and associatedphoto-oxidizing and reducing agents, optional additives to promotecrosslinking or other desirable properties, and a suitable solvent. Thematrix-forming polymer may be a thermoplastic, a thermoset, anelastomer, or a mixture of polymers, optionally mixed with crosslinkers(i.e., thermosettable precursors), plasticizers, or other desirableadditives, etc. A “suitable solvent” may be a solvent capable ofdissolving the polymer to form a polymer solution that is homogeneous ona macroscopic scale and is free-flowing. The polymer may be solvated toa concentration between, for example, about 0.5 wt % and about 90 wt %.For example, the polymer may be solvated at as high a concentration aspossible where solution atomization or break-up into droplets is stillachievable, such as by atomization or suspension and agitation in asecond immiscible liquid. This may lead to solutions with a polymercontent, for example, between about 10 wt % and about 50 wt %.

In one embodiment of this process, the formation of droplets may beachieved by atomizing the polymer solution (with the other componentssuch as the image-forming agents, photo-oxidizing and reducing agents,etc.) into a drying gas atmosphere where solvent removal proceeds bysimple evaporative drying. In this embodiment, the droplets may beautomatically cooled as the solvent evaporates due to the latent heat ofvaporization associated with such a phase change. Such atomizationtechniques may include, for example, high-pressure atomization,two-fluid atomization, rotary atomization, ultrasonic atomization, etc.The type of technique used, as well as the operating parameters, willdepend on the desired particle size distribution, the composition of thesolution being sprayed, etc.

Droplet formation may be alternatively accomplished by introducing thepolymer-solvent solution (with the other components such as theimage-forming agents, photo-oxidizing and reducing agents, etc.) into asecond, immiscible liquid in which the polymer is immiscible and thepolymer solvent is only slightly soluble. With agitation the polymersolution may be broken up into dispersed droplets, forming a suspensionof polymer solution droplets distributed within the second liquid. Thesecond liquid may be chosen such that it is not a solvent for thepolymer, and is somewhat incompatible with the polymer solvent such thatthe overall polymer solution is dispersible as discrete droplets withinthe second liquid. The second liquid should provide a reasonablesolubility for the polymer solvent such that the polymer solvent isextracted from the droplets in a manner analogous to evaporative drying.Once sufficient solvent has been removed, the polymer will phaseseparate and form a polymer matrix at the droplet surface, as in thecase of evaporative drying. Further extraction of the solvent results inparticulates comprising the polymer material. The extent to which othercomponents (image-forming agents, photo-oxidizing and reducing agents,etc.) remain in the droplets during solvent extraction will depend onthe component's diffusivity in the polymer and compatibility with thepolymer, etc. Components such as crosslinkers, catalysts, plasticizers,pigments, etc., will generally remain within the droplet upon solventremoval since these agents are typically chosen to be compatible withthe polymer or polymer solvent. When the particulates have sufficientlysolidified, they may be collected by filtration, centrifugation,sedimentation, flotation, or other separation methods known in the art.

This second liquid may be advantageously water, as many polymer solventsare immiscible and only slightly soluble in water. Other examplesinclude hydrophobic liquids such as fluorocarbons, silicone fluids, etc.Emulsifying agents may also be added to the second liquid or the polymersolution to promote and stabilize the suspension and particle sizedistribution of polymer solution droplets.

Utilizing these of embodiments of this process, a final productcomprising dual wavelength image-forming particulates having a flowable,dispersible, residue-free, thermoplastic or thermosetting may beobtained. The polymer, co-polymer, or polymer blend may be chosen fromany existing polymers, provided there exists a suitable solvent capableof dissolving the polymer. The particulates may possess reactivefunctionalities, either built into the polymer chains or added to theformulation in the form of crosslinking or other reactive groups, thatallow the particulates to fuse to each other or to a surrounding matrixduring subsequent use.

Embodiments a process of the present invention are further illustratedin FIGS. 1-2. Referring to FIG. 1, an embodiment of a processillustrating the steps for preparing dual wavelength imagingcomposition, for coating a paper web with a dual wavelength imagingcomposition according to the present invention using a metering rod sizepress, and for imaging of the coated paper is shown, as indicatedgenerally as 100. Process 100 includes the initial step 102 of forming apolymer solution. This polymer solution from step 102 may be used toform a solid polymer in the form of a sheet, film, etc., of polymer, asindicated by 104, or may be sprayed, as indicated by 106, to formpolymer particulates, which may then be dispersed in starch in watermixture, as indicated by step 108. The solid polymer 104 may be coarselyground, as indicated by step 112, dispersed in a solvent (e.g., water),as indicated by step 116, to form a slurry, and then wet slurry ground,as indicated by step 120. Alternatively, solid polymer 104, after coarsegrinding in step 112, may be subjected to cryogenic grinding, asindicated by step 124, and then dispersed in a solvent (e.g., water), asindicated by step 128. As further shown in FIG. 1, the wet slurry groundpolymer particulates from step 120, the cryogenic ground and dispersedpolymer particulates from step 128, or the sprayed and dispersed polymerparticulates from step 108 may be coated, as indicated by step 132, ontoone or both sides or surfaces of paper web by using, for example, a rodmetering size press. This coated paper web may then be exposed, asindicated by step 136, to form one or more images on the coated paperweb.

An embodiment of the method of the present invention for coating a paperweb with a dual wavelength imaging composition is further illustrated inFIG. 2. Referring to FIG. 2, an embodiment of a system for carrying outan embodiment of the method of the present invention is illustratedwhich may be in the form of, for example a rod metering size pressindicated generally as 200. Size press 200 may be used to coat a paperweb, indicated generally as 204. Web 204 moves in the directionindicated by arrow 206, and which has a pair of opposed sides orsurfaces, indicated, respectively, as 208 and 212.

Size press 200 includes a first assembly, indicated generally as 214,for applying the dual wavelength imaging composition to surface 208.Assembly 214 includes a first reservoir, indicated generally as 216,provided with a supply of a dual wavelength imaging composition,indicated generally as 220. A first take up roll, indicated generally as224 which may rotate in a counterclockwise direction, as indicated bycurved arrow 228, picks up an amount of the dual wavelength imagingcomposition from supply 220. This amount of dual wavelength imagingcomposition that is picked up by rotating roll 224 may then betransferred to a first applicator roll, indicated generally as 232,which rotates in the opposite and clockwise direction, as indicated bycurved arrow 236. (The positioning of first take up roll 224 shown inFIG. 2 is simply illustrative and roll 224 may be positioned in variousways relative to first applicator roll 232 such that the dual wavelengthimaging composition is transferred to the surface of applicator roll232.) The amount of dual wavelength imaging composition that istransferred to first applicator roll 232 may be controlled by meteringrod 244 which spreads the transferred composition on the surface ofapplicator roll 232, thus providing relatively uniform and consistentthickness of a first dual wavelength imaging coating, indicated as 248,when applied onto the first surface 208 of web 204 by applicator roll232.

As shown in FIG. 2, size press 200 may also be provided with a secondassembly indicated generally as 252, for applying the dual wavelengthimaging composition to surface 212. Assembly 252 includes a secondreservoir indicated generally as 256, provided with a second supply of adual wavelength imaging composition, indicated generally as 260. Asecond take up roll, indicated generally as 264 which may rotate in aclockwise direction, as indicated by curved arrow 268, picks up anamount of the dual wavelength imaging composition from supply 260. Thisamount of dual wavelength imaging composition that is picked up byrotating roll 264 may then be transferred to second take up roll,indicated generally as 272, which rotates in the opposite andcounterclockwise direction, as indicated by curved arrow 276. Asindicated in FIG. 2 by the dashed-line box and arrow 280, second take uproll 264 may be positioned in various ways relative to second applicatorroll 272 such that the dual wavelength imaging composition istransferred to the surface of applicator roll 272. The amount of dualwavelength imaging composition that is transferred to second applicatorroll 272 may be controlled by a second metering rod 284 which spreadsthe transferred composition on the surface of applicator roll 272, thusproviding relatively uniform and consistent thickness of the second dualwavelength imaging coating, indicated as 288, when applied onto thesecond surface 212 of web 204 by applicator roll 272.

It should be appreciated that the embodiments illustrated in FIGS. 1 to2 are provided to illustrate the teachings of the present invention.Alterations or modification within the skill of the art of theembodiments in FIGS. 1 to 2 are considered within the scope of thepresent invention, so long as these alterations or modifications operatein a same or similar manner, function, etc.

In one embodiment of the present invention, the polymer material may bea cellulose ester such as cellulose acetate butyrate. In one embodiment,the polymer material may comprise from about 40 to about 99% of thesolids portion of dual light imaging composition of the presentinvention. In another embodiment, the polymer material may compriseabout 50 to about 99% of the solids portion in the dual light imagingcomposition.

In one embodiment, a photo-oxidizing agent may comprise about 1 to about10%, while the reducing agent comprises from about 0.2 to about 6%, ofthe solids portion of the dual wavelength imaging composition of thepresent invention. In another embodiment, the photo-oxidizing agent maycomprise about 2 to about 6%, while the reducing agent comprises fromabout 1 to about 3%, of the solids portion of the dual wavelengthimaging composition of the present invention.

In one embodiment, one or more leuco dyes may collectively comprise fromabout 0.1 to about 10% of the solids portion of a dual light imagingcomposition of the present invention. In one embodiment, one or moreleuco dyes may collectively comprise from about 1 to about 5% of thesolids portion of a dual light imaging composition of the presentinvention.

In one embodiment, acids/couplers may collectively comprise about 0.1 toabout 20% of the solids portion of a dual light imaging composition ofthe present invention. In one embodiment, acids/couplers maycollectively comprise from about 1 to about 6% of the solids portion ofa dual light imaging composition of the present invention.

In one embodiment, at least some of the particulates may be about 10microns or less in diameter. In another embodiment, at least some of theparticulates may be about 5 microns or less in diameter. In yet anotherembodiment, at least some of the particulates may be about 3 microns orless in diameter.

In one embodiment of the present invention, imaging-forming particulatesmay be prepared from a formulation shown in the following table:

TABLE 1 Useful Typical Range (%) Range (%) Polymer Materials 40-99 50-80Plasticizers  0-45 10-20 Oxidizing Agents  1-10 2-6 Leuco dyes 0.1-10 1-3 Acids/Couplers 0.1-20  1-6 H-donors (Electron Donor Agents)  4-20 8-15 Reducing Agents 0.2-6   1-3

In one embodiment of the present invention, imaging-forming particulatesmay be prepared using an organic solvent in order to homogenize all ofthe ingredients shown in the above table and to provide a solutionthereof. This solution may then be cast in order to remove the solvent,thus forming large polymeric particulates. These larger particulates maythen be broken up, wet ground in water/starch slurry to obtain asmaller, finer particle size (e.g., about 10 microns or less, forexample, about 5 microns or less, or about 3 microns or less) of thepolymeric particulates entrapping the color sensitive formulation, toprovide the imaging composition. This dispersion of imaging compositionmay be used to treat (e.g., coat) a substrate surface (e.g., paper websurface) a substrate surface (e.g., paper web surface) surface using rodmetering size press, followed by drying, etc. This treated substrate(e.g., coated paper web) may then be subjected to a first wavelength oflight (e.g., in the range of from about 300 to about 350 nm) to activateand cause the formation of images, followed by subjecting the activatedsubstrate (e.g., paper web) to a second wavelength of light (e.g., inthe range of from about 360 to 450 nm) to termination the formation ofimages on the surface of the substrate (e.g., paper web).

EXAMPLES Example 1

Dual wavelength image-forming particulates may be prepared as follows:

Spray Equipment:

The particulates may be sprayed using two types of spraying equipment.For small quantities of material (e.g., 20 grams of solids dissolved in200 grams of solvent), a Preval portable Spray Gun #267 (Precision ValveCorporation, Yonkers, N.Y.) is used. This is a hand-held device thatuses an aerosol spray can to pressurize the solution through a 0.8 mmnozzle, producing particles in the 20-50 micron size range (particles oflarger size may also present).

For larger quantities of material (e.g., 1 kilogram of solids in 10kilograms of solvent), a HVLP Spray Gun may be used. This gun may bepressurized by an air compressor, and the pressure of the system may bevaried. It is found that a maximum pressure of the system (approximately45 PSI) may provide the best results. The solution may be sprayed, forexample, for a period of 15 seconds, and then a 45-second break may beneeded to allow the pressure in the system to return back to 45 PSI. TheHVLP Spray Gun may use a 1.4 mm nozzle, and may provide particles in the10-20 micron size range with occasional larger particles (20-50microns). The spray gun may also provide a mechanism for regulating theratio of liquid to air as the solution is introduced into the nozzle. Byadjusting this knob, it may be possible to produce particles in the 10micron range with virtually no particles bigger than 20 microns. Usingthese liquid/air parameters may require larger amounts of air relativeto liquid, thus requiring longer operating times.

For larger scale applications, the aforementioned method of spraying maybe used. This method is referred to as the “two fluid nozzle spray”method. Another type of spraying method that may be used on theindustrial scale is called the “rotary atomization spray” method. Thistechnique uses a pressurized main feed that exits through round atomizerrotating at a high speed.

Solvent:

For spraying small quantities of materials, methylene chloride may beused as the solvent. The ingredients used in the formulations may bedissolved in methylene chloride. For small scale sprays with adisposable Preval gun, methylene chloride may be used since the aerosolcan run out before the solvent could do any appreciable damage to thespray gun. When spraying larger amounts of material, a solvent such asacetone may be used. Acetone dissolves the components fairly well, and anice powder may be obtained after spraying.

Acetone may react with p-toluenesulfonic acid (PTSA) due to anacid-catalyzed condensation of the acetone. To minimize the chances ofthis happening, the PTSA may be the last ingredient added when themixture is being prepared. By maintaining cooler temperatures, keepingthe concentration of PTSA to a minimum and limiting the time the twoingredients are in contact with each other, this potential reaction maybe avoided.

Container for Collecting the Spray:

For small scale quantities, a cardboard box lined with tinfoil may beused to collect the spray. The box used to collect the spray from thePreval hand sprayer may be, for example, 15 inches high, 22 inches wideand 20 inches in length. The box may be placed in a fume hood, and thesolution may be sprayed horizontally into the box. Alternatively, thebox may be, for example, 48 inches high, 22 inches wide and 31 inchesdeep. This taller box allows for a longer “time of flight” for thedroplet, giving the solvent more time to evaporate. The result is that adry powder may be collected on the bottom floor of the box, instead of apaste consisting of solvent and powder. Once the dry powder is produced,it may be collected by scraping off the material.

Another box constructed of stainless steel sheets may also be used withthe HVLP spray gun. This box may be, for example, 24 inches wide and 48inches high to provide the needed time of flight for the droplet toevaporate. In addition, this box may be expanded to 40 inches in lengthto accommodate the HVLP sprayer. At a shorter length, the powder maystick to the back wall of the box as the forward thrust from the HVLPgun is greater than that of the Preval sprayer.

In addition, an outlet pipe may be constructed at the bottom of thecontainer to allow the evaporated solvent to exit the box. This pipethen exits into a fume hood to allow safe removal of the solvent vapors.This exit pipe is useful when spraying larger amounts of material.Otherwise, the atmosphere within the box may become oversaturated withsolvent. The solvent then condenses at the bottom of the container,forming a paste instead of a powder. Another way to avoid thesesupersaturated conditions is to spray the solution in intervals.

On a small scale, 35% of the solid sprayed may be collected. When theHVLP spray gun is used, the yields may reach as high as 75-80%. Ingeneral, it is easier to recover large amounts of powder as a smallerpercentage is lost clinging to the sides of the box, etc. In a largerscale facility, larger amounts of solvents may be evaporated, and thesevapors may need to be collected and recycled. Condensers may also beneeded along the exit route to ensure that this process occurs. Filtersmay also be needed along the exit path to contain smaller particles ofthe powder that is being deposited, while at the same time allowing thesolvent vapors to escape.

Example 2

The preparation and imaging of a paper web coated with a dual wavelengthimaging composition is as follows:

Step 1—Formulation Dissolution in Solvent

Components of the formulation dissolved in the solvent until completelyhomogeneous solution is obtained. The solvent may be chosen based on thesubsequent workup of the homogeneous solution to obtain smaller particlesizes, by spraying (Step 2, below), casting and grinding (Steps 3, 4 and6 or 7, below), etc. In small laboratory conditions acetone may bechosen for spraying (Step 2), while methylene chloride may be chosen forsolid polymer casting (Step 3).

Step 2—Polymer Particle Production Via Spraying

Parameters such as air pressure, solvent/solids ratio, and spray gunnozzle diameter may be varied to minimize particle size. Particles assmall as 30-50 microns may be obtained.

Step 3—Solid Polymer Production for Subsequent Grinding

Layers of solid polymer forming large pieces may be produced by castingthe solution from Step 1 and air drying. Sufficient time is allowed forcomplete solvent evaporation. Additional time in a vacuum oven may beused to ensure that all of the solvent escapes.

Step 4—Rough Grinding of Solid Polymer Obtained in Large Pieces

Solids obtained on Step 3 may be roughly ground with a coffee grinder toreduce their size below 1 mm.

Step 5—Solid Particle Dispersion

Particles from both Steps 2 and rougher particles from Step 4 may bedispersed in a warm (65° C.) starch/water dispersion. No agglomerationmay occur, but particles may settle due to gravity, especially in thecase of Step 4. Efficient stirring may be employed during dispersionwith the starch/water temperature not exceeding 75° C. Particles may beoptionally dispersed in a surfactant/water mixture with subsequentaddition to a starch/water mixture. The surfactant is used in thesurfactant/water mixture to prevent starch coagulation.

Step 6A—Pathways for Particle Size Reduction—Cryogenic Grinding

Particles obtained on Step 4 may be reduced in size via cryogenicgrinding. Dry particles may be ground in the presence of liquidnitrogen. If cryogenic grinding is used, the solid particles obtainedmay need to be further dispersed for easy delivery at the mill (see Step6B below).

Step 6B—Pathways for Particle Size Reduction—Wet Slurry Grinding

Wet grinding in the presence of ceramic media may be carried out on ahorizontal mill. Wet media may be provided from a starch/waterdispersion obtained from Steps 4 and 5. By using wet grinding, aparticle/starch/water slurry may be obtained which is ready to bedelivered to the mill. Parameters in wet grinding may include: the timein the mill, the ceramic media used, the ceramic media/particle loadingratio, the mill rotation speed, etc.

Two-step wet grinding may be used if dispersed particles from Step 4 areused. Starting with the Step 4 particles, a slurry with at least some ofthe particles having a particle size below 10 microns (e.g. below 5microns) may be obtained in 4-5 hrs.

Step 7—Coating with Rod Metering Size Press

Particles from Step 6A or 6B may be coated on a paper web using a rodmetering size press, yielding an even and smooth coating on paper.

Step 8—Exposure

The coated paper web from Step 7 may be subjected to a first wavelengthof light (e.g., in the range of from about 300 to about 350 nm) toactivate and cause the formation of images, followed by subjecting theactivated paper web to a second wavelength of light (e.g., in the rangeof from about 360 to 450 nm) to terminate the formation of images on thesurface of the paper web.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

What is claimed is:
 1. A process comprising the following steps: (a)providing a substrate having first and second surfaces; and (b)providing a plurality of dual wavelength imaging particulates, whereinthe particulates each comprise a polymeric matrix of polymer material inwhich is contained: one or more imaging agents comprising a lightactivated dye; a photo-oxidizing agent which is activated at a firstwavelength of light to cause the one or more image-forming agents toform one or more images in or on the substrate; and a reducing agentwhich is activated at a second wavelength of light to cause terminationof the formation of the one or more images; and (c) treating at leastone of the first and second surfaces of the substrate of step (a) withthe particulates of step (b).
 2. The process of claim 1, wherein thesubstrate of step (a) comprises a paper web and wherein step (b) iscarried out with a metering size press to treat at least one surface ofthe paper web with the particulates of step (b).
 3. The process of claim1, wherein the polymer material of each particulate of step (b)comprises cellulose acetate butyrate.
 4. The process of claim 1, whereinthe one or more imaging agents of step (b) comprise a leuco dye.
 5. Theprocess of claim 1, wherein each particulate of step (b) furthercontains one or more acids/couplers.
 6. The process of claim 1, whereinthe photo-oxidizing agent of step (b) is activated at a wavelength inthe range of from about 300 to about 350 nm, and wherein the reducingagent of step (b) is activated at a wavelength in the range of fromabout 360 to about 450 nm.
 7. A process for making a dual wavelengthimaging composition comprising the following steps: (a) providing asolvent; and (b) dispersing a plurality of dual wavelength image-formingparticulates in the solvent to form a dual wavelength imagingcomposition, wherein each particulate of the plurality of particulatescomprises a polymeric matrix of polymer material in which is contained:one or more image-forming agents comprising a light activated dye; aphoto-oxidizing agent which is activated at a first wavelength of lightto cause the one or more image-forming agents to form one or moreimages; and a reducing agent which is activated at a second wavelengthof light to cause termination of the formation of the one or moreimages.
 8. The process of claim 7, wherein the solvent of step (a)comprises water.
 9. The process of claim 7, wherein the polymer materialof each particulate of step (b) comprises cellulose acetate butyrate.10. The process of claim 7, wherein the polymer material comprises fromabout 40 to about 99% of the solids portion of the imaging compositionof step (b).
 11. The process of claim 7, wherein the one or more imagingagents of step (b) comprise a leuco dye comprising from about 0.1 toabout 10% of the solids portion of the imaging composition.
 12. Theprocess of claim 7, wherein at least some of the particulates of step(b) are about 10 microns or less in diameter.
 13. The process of claim12, wherein at least some of the particulates of step (b) are about 5microns or less in diameter.
 14. The process of claim 7, wherein theparticulates of step (b) are formed by the steps of: (c) coarselygrinding solid polymer material to form coarsely ground particulates;and (d) cryogenically grinding the coarsely ground particulates.
 15. Aprocess for making a dual wavelength imaging composition comprising thefollowing steps: (a) providing a solvent; and (b) dispersing a pluralityof dual wavelength image-forming particulates in the solvent to form adual wavelength imaging composition, wherein each particulate of theplurality of particulates comprises a matrix of polymer material andcontains: one or more image-forming agents; a photo-oxidizing agentwhich is activated at a first wavelength of light to cause the one ormore image-forming agents to form one or more images; and a reducingagent which is activated at a second wavelength of light to causetermination of the formation of the one or more images; wherein theparticulates of step (b) are formed by the steps of: (c) coarselygrinding solid polymer material to form coarsely ground particulates;(d) dispersing the coarsely ground particulates in starch in watermixture to form a slurry; and (e) wet slurry grinding the dispersedparticulates to provide the particulates of step (b).